Recently, there has been interest in minimally invasive and percutaneous replacement of cardiac valves. In the specific context of pulmonary valve replacement, for example, U.S. Patent Application Publication Nos. 2003/0199971 A1 and 2003/0199963 A1, both filed by Tower, et al. and incorporated herein by reference, describe a valved segment of bovine jugular vein, mounted within an expandable stent, for use as a replacement pulmonary valve. The replacement valve is mounted on a balloon catheter and delivered percutaneously via the vascular system to the location of the failed pulmonary valve and expanded by the balloon to compress the native valve leaflets against the right ventricular outflow tract, thereby anchoring and sealing the replacement valve.
As described in the articles: “Percutaneous Insertion of the Pulmonary Valve”, Bonhoeffer, et al., Journal of the American College of Cardiology 2002; 39: 1664-1669 and “Transcatheter Replacement of a Bovine Valve in Pulmonary Position”, Bonhoeffer, et al., Circulation 2000; 102: 813-816, both incorporated herein by reference in their entireties, the replacement pulmonary valve may be implanted to replace native pulmonary valves or prosthetic pulmonary valves located in valved conduits. Other articles that describe features of percutaneous valve implantation include Louise Coats, et al., “The Potential Impact of Percutaneous Pulmonary Valve Stent Implantation on Right Ventricular Outflow Tract Re-Intervention,” European Journal of Cardio-Thoracic Surgery (England), April 2005, pgs. 536-43; Peter C. Block, et al., “Percutaneous Approaches to Valvular Heard Disease,” Current Cardiology Reports (United States), March 2005, pgs. 108-13; Georg Lutter, et al., “Percutaneous Valve Replacement: Current State and Future Prospects,” Annals of Thoracic Surgery (Netherlands), December 2004, pgs. 2199-206; Younes Boudjemline, et al., “Percutaneous Pulmonary Valve Replacement in a Large Right Ventricular Outflow Tract: An Experimental Study,” Journal of the American College of Cardiology (United States), Mar. 17, 2004, pgs. 1082-7; S. Khambadkone, et al., “Percutaneous Implantation of Pulmonary Valves,” Expert Review of Cardiovascular Therapy (England), November 2003, pgs. 541-18; Y. Boudjemline, et al., “Percutaneous Valve Insertion: A New Approach,” Journal of Thoracic and Cardiovascular Surgery (United States), March 2003, pgs. 741-2; Philipp Bonhoeffer, et al., “Percutaneous Insertion of the Pulmonary Valve,” Journal of the American College of Cardiology (United States), May 15, 2002, pgs. 1664-9; Younes Boudjemline, et al., “Steps Toward Percutaneous Aortic Valve Replacement,” Circulation (United States), Feb. 12, 2002, pgs. 775-8; P. Bonhoeffer, et al., “Percutaneous Replacement of Pulmonary Valve in a Right-Ventricle to Pulmonary-Artery Prosthetic Conduit with Valve Dysfunction,” Lancet (England), Oct. 21, 2000, pgs 1403-5; P. Bonhoeffer, et al., “Transcatheter Implantation of a Bovine Valve in Pulmonary Position: A Lamb Study,” Circulation (United States), Aug. 15, 2000, pgs. 813-6; G. O. Yonga et al., “Effect of Percutaneous Balloon Mitral Valvotomy on Pulmonary Venous Flow in Severe Mitral Stenosis,” East African Medical Journal (Kenya), January 1999, pgs. 28-30; and G. O. Yonga, et al., “Percutaneous Transluminal Balloon Valvuloplasty for Pulmonary Valve Stenosis: Report on Six Cases,” East African Medical Journal (Kenya), April 1994, pgs. 232-5, all of which are also incorporated herein by reference in their entireties.
The approach to pulmonary valve replacement described in the above patent applications and articles remains a viable treatment for certain patients. In particular, the Melody valve is a commercial form of a pulmonary valve replacement available from Medtronic, Inc. that is usable according to the above noted approach. Other techniques have also been developed to broaden those patients that can benefit from such pulmonary valve replacement procedures including the provision of other size valves than those of sizes that can be created from the size range of available valved segments of bovine jugular veins.
A delivery system that is associated with the Melody pulmonary valve is also commercially available from Medtronic, Inc. The Melody delivery system is a catheter system that includes an inflatable balloon at a distal end of the device onto which the pulmonary valve replacement is crimped. This system is designed for control and steerability from a proximal end of the device for guiding the pulmonary valve replacement to position within a patient's heart via the patient's vasculature. In particular, this system is designed for deployment by the balloon at the patient's native pulmonary valve annulus as accessed via the femoral vein of the patient. The valve is typically sheathed as crimped directly onto the distal balloon of the delivery system and includes the ability to slide the sheath from covering the collapsed replacement valve so that the balloon can thereafter be expanded for permanently deforming and expanding the metal structure of the replacement valve into a permanent position at the pulmonary valve annulus.
Percutaneous aortic valve replacement procedures are also being investigated. One such valve that has been successfully deployed from a catheter delivery system is the CoreValve aortic valve and system, that is also available from Medtronic, Inc. The CoreValve aortic valve replaces the aortic valve in patients with severe aortic stenosis. The valve leaflets are provided by utilizing a porcine pericardial valve that is sutured to the expandable metal frame. This expandable metal frame, however, utilizes Nitinol metal allow so that the frame and thus the aortic valve is self-expanding for controlled deployment at the aortic valve annulus. This frame structure is typically around 5 cm long and is shaped along its length with a non-uniform diameter for improved anchoring of the aortic valve in position at the valve annulus. Further disclosure of aspects of the CoreValve aortic valve and delivery system are provided within U.S. Pat. Nos. 7,682,390, 7,780,726 and 7,892,281.
Delivery of the CoreValve aortic valve prosthesis or any other percutaneous and self-expandable aortic valve prosthesis typically requires a movable sheath at the distal end of a delivery system that maintains a compressed valve prosthesis beneath the sheath. Retraction of the sheath in a proximal direction of the delivery system as controlled from the proximal end of the delivery system is controlled for deploying the self-expandable valve prosthesis from one end thereof to another. Specifically, a distally positioned end of the valve prosthesis initially expands as the sheath is retracted while a proximally positioned end of the valve prosthesis remains collapsed within the confines of the sheath. A gradual expansion is thus controlled so that the full prosthetic valve is deployed in position, such as at a particular valve annulus. Typically, controlled expansion is conducted by maintaining the prosthetic valve as positioned on the distal end of the delivery system at a precise position, such as determined by fluoroscopy, while sliding the sheath proximally relative to the prosthetic valve and distal end of the delivery system. Self-expansion of the valve prosthesis deploys the prosthesis in this precise position and expansion of the metal frame of the prosthetic valve anchors the prosthetic valve in place. The sliding movement of the sheath can be conducted manually by a surgeon, for example, and such movement can be facilitated and controlled by mechanical means incorporated within a handle at the proximal end of the delivery system.
One such delivery system that has been designed for delivery of a self-expanding valve prosthesis is the AccuTrak™ delivery system that is commercially available from Medtronic, Inc. and is provided as a part of a system including the CoreValve aortic valve prosthesis, discussed above. The Accutrak delivery catheter system is a single use, intravascular “over the wire” delivery catheter designed specifically to be used with the Medtronic CoreValve percutaneous aortic valve. The Accutrak system incorporates a protective deployment sheath that houses and deploys the aortic valve prosthesis. The Accutrak system includes an integrated handle designed to provide the user with accurate and controlled deployment. After the deployment system is placed in the vicinity of the aortic annulus, the user retracts the deployment sheath, thereby deploying the prosthetic aortic valve to the desired location. The system includes a micro-control thumb wheel and a macro-control slide, each of which are independently provided to the control handle thereof. In use, the deployment sheath can be partially pulled back to evaluate the PAV location prior to fully releasing the PAV. In this way, the user can make slight adjustments to the PAV location if needed prior to release.